Activation of mitogen-activated protein kinase (MAPK) modules by different stimuli regulate many important cell functions, including differentiation, mitogenesis, apoptosis/survival, and gene expression. Multiple MKKKs, MKKs and MAPKs have now been described and despite some apparent redundancy, these modules demonstrate remarkable specificity and functional importance. This proposal focuses on one such module, MEKK2-MEK5-ERK5, and its importance in cytokine regulation in mast cells and T lymphocytes. In mast cells, MEKK2 has been shown to play an essential role in the activation of JNK and ERK5 following occupancy of mast cell surface receptors (FceRI, Kit or IL-3). MEKK2 is essential for the transcriptional regulation of a number, but not all, cytokines released by these cells. This application proposes to delineate the role of MEKK2 and ERK5 in mast cell function, especially as it pertains to the development of allergen-induced airway inflammation and hyperresponsiveness. In addition, the role of MEKK2 and ERK5 in T cell regulation of cytokine production will be defined. In the previous funding period we accomplished the targeted disruption of the MEKK2 gene. We now propose to make a conditional ERK5 knockout to define the function of ERK5 in controlling mast cell and T lymphocyte cytokine production. The specific aims of this proposal include: 1) to define the role of the adaptor protein Lad in coupling MEKK2 and ERK5 activation to regulation by tyrosine kinases, 2) to define the function of MEKK2and ERK5 in the control of mast cell and T lymphocyte cytokine production; and 3) to define the role of Lad,MEKK.2 and ERK5 in the development of airway inflammation and hyperresponsiveness with an emphasis on mast cell dependence of these responses. Cumulatively, these studies will provide critical insight into the regulation of cytokine expression contributing to allergic inflammation in the lung and potentially other target organs. The studies will also define MEKK2 and ERK5 as targets for drug discovery for the control of allergic inflammation.